Area Forecast Discussion
Issued by NWS State College, PA

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338 FXUS61 KCTP 180909 AFDCTP Area Forecast Discussion National Weather Service State College PA 409 AM EST Thu Jan 18 2018 .SYNOPSIS...
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A large are of high pressure centered over the Lower Mississippi Valley will ridge northeast across the Ohio River Valley and into the Mid Atlantic states today. This weather feature will maintain fair skies but cold temperatures. Temperatures will moderate to near normal Friday, then climb well above normal over the upcoming weekend with mainly dry weather continuing. The next chance for widespread rain showers will come Monday into Tuesday with the passage of a cold front.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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GOES16 and regional sfc obs indicates a shallow layer of orographic stratus and stratocu located near and to the west of the Route 219 corridor (along the spine of the Alleghenies) early this morning. Model soundings show this cloud layer occupying the thermal channel of -12 to -18C, which is right in the middle of the prime Dendritic Growth Zone. We see confirmation of this with some very light...4SM -snow being reported at KJST. Flurries from this cloud layer are expected through 17Z today before temps warm by several deg C in this layer and mixes out a bit. Over the Central and Eastern parts of our CWA today, mainly clear skies and light wind allowed temps to dip into the single digits, and even near or slightly below zero F throughout some protected valley locations across the Middle Susq Valley where a deep fresh snowpack is found. Later on and elsewhere today, periods of sct-bkn altocu and cirrus will spill southeast from the glakes as deep layer warm advection begin with the slow departure of the anomalously deep, snow-producing sfc and upper low near the Outer Banks. Highs this afternoon will be about 5 deg F below normal, and range from near 20F across the NW mtns to the L30s in the Southeast. Westerly winds will freshen to 10 to 15 kts today, with gusts in the 25 to 30 kts range later this morning and this afternoon over the higher terrain of SC and SW PA. Relatively lighter winds will occur across the eastern zones. The wind will create a wind chill 15 to 20 degrees F lower than the actual air temp through today.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
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Variable amounts of mainly mid and high clouds along with dry conditions will prevail tonight. A slightly lighter westerly breeze with significantly lower gusts will result in wind chills staying steady (or rising slightly) into tonight. Lows tonight will be in the teens, to near 20F in the southern PA valleys. Mid and high clouds increase a bit Friday as do temps, that will climb to slightly above normal highs.
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&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
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High pressure moving off the southeast coast late in the week will bring mild and dry weather to the area which will last through most or all of the upcoming weekend. A deep low will swing a cold front across the area late Monday and early Tuesday next week, accompanied by a few period of rain showers amounting to 1 to 3 tenths of an inch of Liq Equiv precip. There is a low probability for a weak wave of low pressure to develop along the front heading into Tuesday which could add a few to svrl tenths more and even some light accums of snow. Mainly dry weather with just some isolated to scattered snow showers will follow for Tuesday and Wednesday, with temps falling to a few deg below normal by the middle of next week.
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&& .AVIATION /09Z THURSDAY THROUGH MONDAY/... There continues to be some lingering MVFR over my western higher elevation terminals with even some very light snow causing visibilities under 2 miles at JST. Drier air will limit the extent of the low clouds moving out of the mountains, but these high elevation sites may be stubborn to improve despite an overall fair weather pattern. It will be breezy with gusts in the 10-20 mph range. Outlook... Thu...Mainly VFR. Breezy. Fri-Sun...Mainly VFR. Mon...Reduced conditions with rain showers associated with an approaching cold front. && .HYDROLOGY... The threat of ice jamming is diminishing. Dry and colder weather into mid week will form additional ice as stream flows and open channels decrease. Another warm up is expected by the end of the week into the weekend with rain to accompany a frontal system early next week. Dewpoints not fcst to be as high as last Friday evening, so expecting less rain and runoff. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Lambert/Martin AVIATION...La Corte/Ceru HYDROLOGY...Lambert

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